Primer is the most profitable step in a makeup routine and the most often unnecessary, which is not a coincidence. The promise — smoother skin, longer wear — is vague enough that almost any product can make it, and vague promises are hard to disprove.
So be literal about what is in the bottle, because there are only three mechanisms. Blurring primers are silicone-elastomer films that scatter light across an uneven surface, which softens how a pore or fine line reads for a few hours. Grip primers are tacky polymer films that give your base something to adhere to, which genuinely extends wear where makeup slides. Hydrating primers are moisturizers with better marketing — they stop your skin drinking the water out of your foundation.
Notice what is absent: nothing in that list fills a wrinkle, and nothing in it makes your skin better. A primer is a layer between your skin and your base that does one specific mechanical job.
Which matters more over 50 than it would at 30, because an unnecessary layer is not free. Every film on a face that creases is another thing to crack along a fold, and every product is another container to open. The default should be no primer, with one added only when you can say what it is for.
The test below settles it in five minutes, on your own face, which is better evidence than anything a review site can offer.